Considerable experimentation and development in water or hydroponic culture have brought hydroponics to the point where it is expected that hydroponic agriculture will soon represent a minor, but significant, proportion of agricultural production, particularly with respect to certain crops, such as lettuce. The advantages of hydroponics include shortening the growing period of plants from seed germination to plant maturity and the ability to move hydroponically grown plants with great ease and with substantially no damage to the root structures of the plants, whereby the plants may be rearranged to maximize the use of space during all stages of their growth cycle. Hydroponic growing systems, such as that described in U.S. Pat. No. 4,028,847, recognize that plants require more room as they grow and provide for the spreading of the growing plants so that they may be as densely grown during all stages of their growth cycle as is practical and is consistant with generally optimal growing conditions of the plant.
Shortening of the growth cycle of the plant in combination with attendent space efficiencies of hydroponics substantially increase the production per unit area, and considering that hydroponic agriculture is generally carried out in covered structures, such as greenhouses, the total yearly yield per unit area is much higher than the yield of seasonal, soil-based agriculture.
The recognized advantages of hydroponics are counterbalanced by the costs of hydroponic growing including initial capital costs, nutient costs and labor costs. A significant labor cost involves the time spent in arranging growing plants to maximize space usage while giving the plants more room as they mature.
Conventionally, plants have been grown hydroponically with the plants supported by various means on beds in which their roots are in contact with aqueous nutrient solution, such as slowly flowing streams or sprays of nutrient solution. In U.S. Pat. Nos. 3,927,491 and 4,037,360, it is asserted that certain advantages accrue by floating plants on pools of nutrient solution. As a means of floating the plants, it is proposed in the '491 and '360 patents that the plants be originally floated on individual small rafts, and after the plants have grown larger, that the plant-containing rafts be nested in individual larger rafts increasing the total buoyancy. A significant disadvantage of the system proposed in the above-mentioned '491 and '360 patents is the labor cost involved in individually nesting each individual small raft in the auxilliary larger raft as each plant matures.
Nevertheless, the concept of hydroponically growing plants by floating them in nutrient tanks has considerable advantages. Large shallow tanks may be simply constructed and provide assurance that roots of all the plants are kept moist and supplied with nutrients. The plumbing required to supply a tank system with nutrient solution is simple, and the nutrient solution for a very large number of plants can be very rapidly adjusted or replaced. A pool of water represents a significant heat sink, providing substantial thermal stability that protects the plant from extreme temperatures and sudden temperature changes. The need continues for more efficient apparatus for hydroponically growing plants on floating beds.